The present invention relates to a wireless communication method and apparatus, more particularly, to a method of synchronizing and forwarding control information between two adjacent nodes in an uplink path of a system having a daisy chain via Common Public Radio Interface (CPRI).
CPRI is an industry standard aimed at defining a specification for the interface of base stations between Radio Equipment Controllers (REC) and Radio Equipment (RE). FIG. 1 shows a topology of a chain 100 including several nodes (102a-102d) connected via the CPRI interface. Node 102a is a REC node, node 102d is a RE node, nodes 102b and 102c can be either a REC node or a RE node. As shown in the node 102b, in order to support a CPRI daisy chain configuration, each node has a pair of CPRI units 104a and 104b connected through their auxiliary interfaces 106a and 106b. The chain 100 can be located in one transmission node, e.g., an eNodeB or a relay node, or across more than one transmission node.
In downlink transmission, a timing flow 108 including sync word, basic frame number and hyper frame number is propagated across the chain 100 and a downlink data flow 110, including IQ data and control words, follows the time flow 108, whereas in uplink transmission, the timing flow 108 is transmitted from one node to another in a point to point fashion, and an uplink data flow 112, including IQ data and control words, does not follow the timing flow 108 when being transmitted from one CPRI unit to another CPRI unit within one REC or RE node. Therefore, e.g., in the REC or RE node 102b, there is a timing difference between the two CPRI units 104a and 104b in uplink transmission, which causes a problem to seamlessly forward the control words coming from the downlink node 102c to the uplink node 102a. 
It is therefore desirable to synchronize the control words with the timing flow in uplink transmission before forwarding the control words to the next node in the chain.